Dry lubrication process and bearing surface



United Staes Patent 3,073,761 DRY LUBRECATIGN PROCESS AND BEARINGSURFAQE Charles P. Covino, 31 Woodmont Ave., Upper Montclair, NJ.No'Drawing. Filed Jan. 26, 1960, Ser. No. 4,609 9 Claims. (L 204-68) Thepresent invention relates to a process for bonding dry lubricants tometal surfaces.

In the past it has been found that molybdenum disulphide, molybdenumditelluride, molybdenum diselenide, tungsten disulphide, titaniumdisulphide, titanium ditelluride and minerals of equivalent physicalstructures have certain anti-friction characteristics when applied tobearing surfaces. McCullough in his US. Patent No. 2,622,993 has taughtthat certain compounds of molybdenum and other metals in its periodictable sequence with sulphur, selenium and tellurium, have unusuallubrication qualities and as such are equivalent to each other undercertain circumstances. Such lubricants have proven to be very effectiveat high temperatures and pressures provide low coefiicients of friction.

Efforts to obtain optimum lubrication and lubrication life had led toefforts to bond these lubricants to metals to lengthen the lubricationlife of these dry lubricants and prolong their advantage. McCullough hasfound one method and Bell, US. Patent No. 2,387,872, both employing apressure or impact technique for extending and improving the lubricatinglife of the dry lubricants having the special characteristics ofmolybdenum disulphide and the related compounds. Bramberry in his US.Patent No. 2,534,408 in another technique taught bonding graphite tobearing surfaces to achieve a more permanent dry lubricating effect byuse of resins as a bonding agent as distinguished from impact techniquesor pressure techniques taught by McCullough and Bell.

According to the present invention dry lubricants having thecharacteristics of molybdenum disulphide in resinous vehicles or othercarriers are coated and bonded to bearing surfaces in hard, unexpzctablylong-lasting coatings capable of resisting high temperatures, greattemperature variations and high pressures all with a low or reducing(under pressure) coefficient of friction. Dry lubricants having thecharacteristics of molybdenum disulphide are bondable in thin layers forlong life on a wide variety of metals and alloys.

The object of the presentation provides a new and improved method ofbonding dry lubricants having characteristics of molybdenum disulphidein thin anti-frictional coats to various metal and metal alloy surfaces.

Other objects and advantages of this invention residing in the novelfeatures of the steps, and combinations of components, will become moreapparent from the description of the specific examples hereinafterfollowing. it will be understood that certain features of the inventionmay be utilized other than as exactly disclosed.

The invention, however, is not intended to be restricted to anyparticular step or steps and/or combination of components, or anyparticular application of such steps and/ or combination of components,or any specific method, or any of. various details thereof, even wherespecifically set forth and described herein, as the same may be modifiedin various particulars or may be applied in varied relations withoutdeparting from the spirit and scope of the claimed invention, practicalexamples embodying certain details of the invention being set forth, butonly for the purpose of complying with the requirement of the statutefor disclosure of operative methods, but without attempting to discloseall of the various ice limits and modifications in which invention mightbe embodied.

Although such novel features as are believed to be characteristic in theinvention are pointed out in the claims, the invention as to its objectsand advantages and manner in which they are carried out, may better beunderstood by reference to the examples and the following information.

The process of the present invention is in particular adapted to .drylubrication coatings on nickel and nickel alloys, steel and steelalloys, titanium, titanium alloys and zirconium alloys also applies tocopper, bronze and other metal customarily used as an antifrictionsurface.

Example .1

An aircraft part made of a nickel alloy such as In conel X which is atrademark for an alloy containing approximately a minimum of 70 percentnickel, approximately 14 percent chromium and small parts of titanium,columbium, aluminum, silicon, manganese, copper and limited amounts ofcarbon and sulphur is cleaned by a vapor blast using 120 mesh abrasivegrit in water suspension material. The vapor blasted metal part is thenrinsed in water, subjected to a 20 percent solution of hydrochloric acidfor 30 seconds, rinsed in water, then subjected to an acid solutioncomprising 10 percent hydrofluoric acid, 30 percent nitric acid in watersolution until all over etched, this often takes approximately 30 to 40seconds. The metal part is then again washed, then given a gold strike,using a direct current of 6 volts at a temperature of F., by dipping ina solution of 5 percent pure gold and 16 ounces potassium cyanide, pergallon for 40 seconds. The part is then gold plated in a solution of oneounce of gold per gallon and 14 ounces of potassium cyanide per gallonin a cold solution; the plating is done at a temperature of 80 F. for 5minutes, employing 80 milliamps per square inch. The metallic is gold 99/2 percent pure. Then the part is rinsed in distilled or demineralizedwater. The next step is to send the metal part through an acetic acidrinse in 10 percent solution of acetic acid. The part is then waterrinsed in a hot distilled or demineralized water bath.

The part is then spray-coated with a molybdenum disulphide lubricantwhose particles are held in suspension in a vehicle of phenolformaldehyde resin or other resinous vehicle to a depth of .0003 of aninch. The part is then oven-cured for one hour at 350 F. and slow cooledfor 4 hours down to room temperature. The same procedure is followed fordry lubricating other nickel alloys such as Hastelloy X which is atrademark for an alloy consisting of approximately 41 percent nickel, 20percent chromium, 8 percent molybdenum, 17 percent iron and smallamounts of cobalt, carbon, silicon and manganese.

' Example 2 A bearing surface of stainless steel to be dry lubricantcoated is subjected to vapor blast, rinsed, subjected to a 30 percentnitric acid for 15 minutes at a temperature of F. and rinsed, thentreated in the same way as inconel X and Hastelloy X. Commencing withthe hydrofiuoric nitric acid bath, steel alloys, titanium alloys andzirconium are treated in the same manner as stainless steel.

Optimum results with various metals have been obtained where in the goldplating step of the gold content is maintained within 10 percent of theone ounce per gallon limit. It has further been found that the bestresults are obtained in the gold plating step where the potassiumcyanide content of the solution is maintained between 14 and 16 ouncesper gallon. The plating is best when there is metallic gold insuspension and an anode to cathode ratio of 3 to 1.

Most effective results with the lubricated parts and the greatestsuccess in the lubricant plating have been obtained where the drylubricant coat is maintained between .0003 and .0005 of an inch.

Slight variations of all steps may be made to accommodate ditferentalloys. A solution of 37 ounces of dry lubricant per gallon in theresinous suspension seems to give the preferred result. Such resins asphenol formaldehyde or silicon resin serve as effective suspensionvehicles.

The gold striking has the effect analogous to a primary coat of paint.An infinitesimal amount of gold is deposited but with a very strongbond.

Variations in use of the strong acid solution is generally dependent,upon the metals to be rinsed. The oven curing time of the sprayed drylubricant varies with the resinous vehicle used, the metal coated andthe demands of the use of the part being coated.

Tests of parts dry lubricated in accordance with the teaching of thepresent invention show unexpected long life of dry lubricant effectunder severe loads of torque and friction under high ambient heats of1000 F.

Further lubricant life under conditions of high heat and stress of heavyload has been found obtainable by the introduction of a silver strikestep and silver plate step prior to the gold strike and gold plating ofa part to be lubricated.

A diluted bath of silver is used of about one half ounce per gallon ofsilver salts to a gallon of solution containing 16 to 18 ounces ofcyanide per gallon for the silver strike then silver is plated toapproximately .0002 an inch. A gold strike is then placed over thesilver and gold plate for .0001 of an inch then the dry lubricant iscoated from .0003 to .0005 for a final coat. The fixing of the drylubricant coating to the metal follows as in the prior examples or byother known means depending on the carrier vehicle used for the drylubricant in the coatmg.

The terms and expressions which are employed are used as terms ofdescription and not of limitation, and there is no intention, in the useof such terms and expressions of excluding any equivalents of thefeatures shown and described or portions thereof, but it is recognizedthat various modifications are possible within the scope of theinvention claimed.

What is claimed is:

1. A process for preparing a lubricated metal-bearing surface suitablefor high heat and high pressure lubrication comprising cleaning themetal bearing surface, applying a gold strike to said cleaned surface,gold plating said gold strike, and coating said plated surface with acoating comprising a dry lubricant in a resin vehicle, and then curingsaid resin.

2. The process of claim 1 in which the dry lubricant is a compound of ametallic element.

3. The process of claim 2 in which the gold plate is applied to athickness of about 0.0001 inch; and in which the dry lubricant ismolybdenum disulfide which is applied in a liquid phenol-formaldehyderesin to a thickness in excess of about 0.0003 inch.

4. The process of claim 3 in which the metal-bearing surface utilized iscleaned and abraded prior to the application of gold to said surface;and in which the lubricantphenol formaldehyde resin coating is appliedto the said gold plated surface by being sprayed thereon.

5. The process of claim 1 in which a silver plate is applied to themetal-bearing surface prior to the application of the gold plate.

6. The process of claim 1 in which the gold plate is electrodepositedfrom a gold-containing aqueous cyanide bath.

7. A bearing surface for high heat and high pressure lubricationcomprising an inner metal bearing surface, an intermediate gold layerhaving a thickness of about 0.0001 inch, and an outer surface comprisinga cured resinous coating containing a dry lubricant.

8. The bearing of claim 7 in which the outer layer is curedphenol-formaldehyde resin having a thickness of between 0.0003 and0.0005 inches and containing molybdenum disulfide as the dry lubricant.

9. The bearing of claim 8 having a thin silver layer between the goldlayer and the inner metal-bearing surface.

References Cited in the file of this patent UNITED STATES PATENTS

1. A PROCESS FOR PREPARING A LUBRICATED METAL-BEARING SURFACE SUITABLEFOR HIGH HEAT AND HIGH PRESSURE LUBRICATION COMPRISING CLEANING THEMETAL BEARING SURFACE, APPLYING A GOLD STRIKE TO SAID CLEANED SURFACE,GOLD PLATING SAID GOLD STRIKE, AND COATING SAID PLATED SURFACE WITH ACOATING COMPRISING A DRY LUBRICANT IN A RESIN VEHICLE, AND THEN CURINGSAID RESIN.